Power converter and power system

Abstract

To improve electricity stability while making use of distributed control.SOLUTION: A power converter is connected to an alternating-current system including an alternating-current supply section, a generating line connected to the alternating-current supply section, and a fluctuating load connected to the generating line. The power converter converts direct-current power outputted from a direct-current power supply section into alternating-current power. The power converter includes a sensor that detects output current and output voltage of the alternating-current power outputted from the alternating-current supply section, and a control section that sets parameter values for control parameters to perform virtual synchronous generator control, based on the detection result of the sensor. The control section obtains the output current and the output voltage from the sensor, identifies the change of the fluctuating load based on the obtained output current and output voltage, and sets parameter values for the control parameters according to the identified change of the fluctuating load.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a power converter and a power system.

Background Art

[0002] Conventionally, as a power system that performs virtual synchronous generator control, so-called VSG (Virtual Synchronous Generator) control, a system including an inverter that executes virtual synchronous generator control and a control device that controls the inverter is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the system of Patent Document 1, a control device separate from the inverter is provided, and the inverter is modulated and controlled by the control device. Here, the inverter may be used in distributed control that does not communicate with devices such as other inverters and a centralized control system outside the inverter in order to enhance versatility. In Patent Document 1, since the inverter is controlled by the control device, it is impossible to perform control of the inverter alone, resulting in a system configuration in which it is difficult to execute distributed control of the inverter. In other words, in Patent Document 1, when attempting to execute distributed control of the inverter, it is impossible to control the inverter by the control device, making it difficult to perform appropriate power conversion by the inverter.

[0005] Therefore, an object of the present disclosure is to provide a power converter and a power system that can improve power stabilization while taking advantage of distributed control.

Means for Solving the Problems

[0006] The power converter of the present disclosure is connected to an AC power system including an AC power supply unit, a bus to which the AC power supply unit is connected, and a variable load connected to the bus, and converts DC power output from a DC power supply unit into AC power. The power converter includes a sensor that detects an output current and an output voltage of the output AC power, and a control unit that sets a parameter value of a control parameter for executing virtual synchronous generator control based on a detection result of the sensor. The control unit acquires the output current and the output voltage from the sensor, identifies a change in the variable load based on the acquired output current and output voltage, and sets a parameter value of the control parameter according to the identified change in the variable load.

[0007] The power system of the present disclosure includes an AC power supply unit, a bus to which the AC power supply unit is connected, a variable load connected to the bus, a DC power supply unit connected to the bus, and converts DC power output from the DC power supply unit into AC power and executes virtual synchronous generator control.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to improve the stabilization of power while taking advantage of decentralized control.

Brief Description of the Drawings

[0009]

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[0010] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited by this embodiment. In addition, the components in the following embodiments include those that can be replaced and are easy for those skilled in the art, or those that are substantially the same. Furthermore, the components described below can be combined as appropriate, and when there are multiple embodiments, the embodiments can also be combined.

[0011] [First Embodiment] The power system 10 according to the first embodiment is a system in which a storage battery 21 as a DC power supply unit and a power converter (hereinafter also referred to as an inverter) 22 are connected to an AC power grid. In this power system 10, the power converter 22 is under decentralized control. The power system 10 will be described with reference to FIG. 1.

[0012] (Power System) FIG. 1 is a diagram regarding the power system according to the first embodiment. The power system 10 includes an AC power supply unit 15, a bus 16, a plurality of variable loads 17, a load 18, a storage battery 21, and an inverter 22.

[0013] The AC power supply unit 15 is, for example, an AC synchronous generator having an inertia function. The AC power supply unit 15 is connected to the bus 16 and supplies the generated AC power to each variable load 17 via the bus 16. The bus 16 is an electric wire through which an alternating current flows. The plurality of variable loads 17 are connected to the bus 16 and are devices that generate loads with a large load power and a short duration. The load 18 is a load other than the variable load 17.

[0014] Here, with reference to FIG. 2, the variable load will be described. FIG. 2 is a graph of an example regarding the load power of the variable load. In FIG. 2, the vertical axis represents the load power and the horizontal axis represents the time. The variable load 17 is, for example, a load accompanied by a steep load fluctuation such as a high-output actuator or a mobile machine tool. As shown in FIG. 2, the plurality of variable loads 17 periodically generate load power, and the magnitudes of the peak values of the load power are different. The plurality of variable loads 17 have a higher load level of the variable load as the load power is larger.

[0015] The storage battery 21 is connected to the bus 16 and supplies the generated DC power to each variable load 17 via the inverter 22 and the bus 16. In the first embodiment, the storage battery 21 is applied as the DC power supply unit, but any device that generates DC power may be used, for example, a device such as a solar power generation device, or a combination thereof may also be used.

[0016] (Inverter) Next, the inverter 22 will be described. The inverter 22 converts DC power into AC power and executes virtual synchronous generator (VSG) control in order to have characteristics equivalent to those of a synchronous generator. The inverter 22 has a sensor that detects the output current and the output voltage, and a control unit 35.

[0017] The sensor includes an ammeter 31 that detects the output current and a voltmeter 32 that detects the output voltage on the output side of the inverter 22. The ammeter 31 and the voltmeter 32 are connected to the control unit 35 and output the current value and the voltage value toward the control unit 35.

[0018] Figure 3 is a diagram related to the control unit of the power converter. As shown in Figure 3, the control unit 35 includes a VSG control unit 36, an output power calculation unit 37, a power fluctuation calculation unit 38, a variable load level identification unit 39, and a control parameter calculation unit 40.

[0019] The VSG control unit 36 is executing virtual synchronous generator control. Also, the VSG control unit 36 has set control parameters for executing virtual synchronous generator control and is executing virtual synchronous generator control according to the set control parameters. The control parameters include an inertia constant for adjusting the frequency fluctuation of the AC power. That is, the inertia constant is a parameter for adjusting the inertia function of the virtual synchronous generator. The larger the inertia constant, the smaller the speed change of the rotational speed and the more difficult it is for the frequency to fluctuate.

[0020] The output power calculation unit 37 acquires the current value i and the voltage value v from the ammeter 31 and the voltmeter 32. The output power calculation unit 37 calculates the output power P based on the acquired current value i and voltage value v. The power fluctuation calculation unit 38 calculates the fluctuation amount ΔP of the output power from the time change of the calculated output power P. The variable load level identification unit 39 identifies the magnitude of the variable load (variable load level L) based on the calculated fluctuation amount Δ of the output power.

[0021] The control parameter calculation unit 40 calculates the inertia constant M as a control parameter based on the magnitude of the identified variable load. Here, the control parameter calculation unit 40 calculates the inertia constant M using the table T shown in FIG. 3. The table T associates the inertia constant M with the variable load level and is obtained in advance through experiments, simulations, etc. The table T is stored in a storage unit (not shown), and the control parameter calculation unit 40 calculates the inertia constant M using the table T. The default value of the table T is the inertia constant M with the smallest value, and multiple levels are set according to the variable load level. Specifically, the inertia constant M is set in four levels, for example, 2 [s], 4 [s], 6 [s], and 8 [s], and is set to a larger value as the variable load level increases.

[0022] In the above inverter 22, when the control unit 35 acquires the current value and voltage value on the output side of the inverter 22, it identifies the variable load level and sets the inertia constant M corresponding to the variable load, so that the frequency of the converted AC power can be made less likely to fluctuate.

[0023] [Second Embodiment] Next, with reference to FIGS. 4 to 6, the second embodiment will be described. FIG. 4 is a diagram related to the control unit of the power converter according to the second embodiment. FIG. 5 is a graph related to the parameters of the estimated variable load. FIG. 6 is a graph related to the pattern of the virtual impedance. In the second embodiment, to avoid duplicate descriptions, the parts different from the first embodiment will be described, and the parts having the same configuration as the first embodiment will be described with the same reference numerals.

[0024] In the power system 10 according to the second embodiment, the control unit 51 of the inverter 22 uses a virtual impedance as a control parameter. The virtual impedance is a parameter for adjusting the power sharing between the AC power supply unit 15 and the storage battery 21. The smaller the virtual impedance, the larger the power sharing on the storage battery 21 side, and the output fluctuations of the AC power supply unit 15 are mitigated.

[0025] As shown in FIG. 4, the control unit 51 includes a VSG control unit (not shown) 36, an output power calculation unit 37, a power fluctuation calculation unit 38, a variable load drive determination unit 52, a variable load parameter identification unit 53, and a virtual impedance calculation unit 54. Since the VSG control unit (not shown) 36, the output power calculation unit 37, and the power fluctuation calculation unit 38 are the same as those in the first embodiment, the description thereof is omitted.

[0026] The variable load drive determination unit 52 determines whether or not the variable load 17 is being driven based on the acquired current value and voltage value and the calculated output power.

[0027] When the variable load drive determination unit 52 determines that the variable load 17 is being driven, the variable load parameter identification unit 53 identifies the load parameters related to the change pattern of the variable load. As shown in FIG. 5, the load parameters include the period T of the variable load, the rising timing T ON of the variable load, the falling timing T OFF of the variable load, and the load power P ON after the variable load rises (when ON). That is, the variable load parameter identification unit 53 estimates the change pattern of the variable load from the calculated output power. In estimating the change pattern of the variable load, for example, information in which the change in the output power (solid line in FIG. 4) and the change pattern of the variable load (dotted line in FIG. 4) are associated in advance by experiments or simulations may be used.

[0028] The virtual impedance calculation unit 54 sets the pattern of the virtual impedance based on the acquired load parameters of the variable load.

[0029] For example, when the change pattern of the variable load is as shown in the upper part of FIG. 5, the virtual impedance calculation unit 54 sets the virtual impedance shown in the lower part of FIG. 5. That is, the virtual impedance calculation unit 54 determines the rising timing T ON of the variable load and the falling timing T OFFIn this case, the value of the virtual impedance (1) is decreased from a predetermined value, and the value of the virtual impedance (2) is set to a predetermined value during the steady state (ON state) after the start-up of the variable load and during the steady state (OFF state) after the shutdown of the variable load.

[0030] In the above inverter 22, when the control unit 51 acquires the current value and voltage value on the output side of the inverter 22, it determines whether the variable load 17 is being driven based on the output power. Then, when the variable load 17 is being driven, the control unit 51 identifies the change pattern of the load power of the variable load, that is, the load parameter of the variable load, and sets the virtual impedance corresponding to the load parameter. By setting the virtual impedance according to the load parameter, the control unit 51 increases the power sharing of the storage battery 21 as the load power of the variable load increases, thereby mitigating the output fluctuations of the AC power supply unit 15.

[0031] [Third Embodiment] Next, with reference to FIGS. 7 to 10, the third embodiment will be described. FIG. 7 is a diagram related to the power system according to the third embodiment. FIG. 8 is an explanatory diagram related to the power supply of the power system. FIG. 9 is a diagram related to the control unit of the power converter according to the third embodiment. FIG. 10 is a graph showing an example of the load power of the variable load. In the third embodiment as well, in order to avoid redundant descriptions, the parts different from the first embodiment and the second embodiment will be described, and the parts having the same configuration as the first embodiment and the second embodiment will be described with the same reference numerals.

[0032] In the power system 60 according to the third embodiment, the control unit 71 of the inverter 22 uses a control gain as a control parameter. The control gain is a parameter for adjusting the responsiveness of the output power.

[0033] As shown in Fig. 7, the power system 60 of the third embodiment is a system in which a plurality of power systems 10 of the first embodiment are connected by tie lines 63. That is, the power system 60 is a system in which a plurality of AC power systems are connected, and is a system capable of supplying power between the AC power systems. In Fig. 7, a power system 60 to which two AC power systems are connected is shown. The symbol of one AC power system is labeled with "a", and the symbol of the other AC power system is labeled with "b". Since each AC power system is the power system 10 of the first embodiment, the description thereof is omitted.

[0034] As shown in Fig. 8, in the power system 60 of the third embodiment, one of the variable loads 17a in one AC power system is in a non-operating state, and the battery 21b in the other AC power system is in a non-operating state. At this time, a situation is assumed in which the battery 21a in one AC power system supplies power L1 to the variable load 17a and also supplies power L2 to the variable load 17b in the other AC power system. Since the impedance of the power supply L2 from the battery 21a to the variable load 17b is larger than that of the power supply L1 from the battery 21a to the variable load 17a, the responsiveness of the power supply may decrease. Therefore, in the power system 60 of the third embodiment, the control unit 71 has the configuration shown in Fig. 9.

[0035] As shown in Fig. 9, the control unit 71 includes a VSG control unit (not shown) 36, an output power calculation unit 37, a power fluctuation calculation unit 38, a remote load power supply determination unit 72, and a current control parameter adjustment unit 73. Since the VSG control unit (not shown) 36, the output power calculation unit 37, and the power fluctuation calculation unit 38 are the same as those in the first embodiment, the description thereof is omitted.

[0036] The remote load power supply determination unit 72 determines whether power is being supplied to the variable load 17b of another AC system based on the acquired current value, voltage value, and the calculated output power. In the determination by the remote load power supply determination unit 72, for example, the response waveform of the output current when power is supplied to the variable load 17b of another AC system is acquired in advance through experiments, simulations, etc., and compared with the acquired response waveform to determine the presence or absence of power supply.

[0037] When the current control parameter adjustment unit 73 determines, based on the determination by the remote load power supply determination unit 72, that power is being supplied to the variable load 17b of another AC system, it sets the control gain so as to improve the responsiveness of the power supply to the variable load 17b of the other AC system. Specifically, as shown in FIG. 10, the control gain is set so that the output power (broken line) of the inverter 22a approaches the load power (solid line) of the variable load 17b. The control gain includes a proportional gain K p and an integral gain K l etc.

[0038] As described above, the power converters and power systems 10 and 60 described in the first to third embodiments are understood as follows, for example.

[0039] The power converter (inverter 22) according to the first aspect is connected to an AC system including an AC power supply unit 15, a bus bar 16 to which the AC power supply unit 15 is connected, and a variable load 17 connected to the bus bar 16. In the power converter that converts DC power output from a DC power supply unit (storage battery 21) into AC power, a sensor (ammeter 31 and voltmeter 32) that detects the output current and output voltage of the output AC power, and a control unit 35 that sets parameter values of control parameters for executing virtual synchronous generator control based on the detection results of the sensor. The control unit 35 acquires the output current and the output voltage from the sensor, identifies the change in the variable load based on the acquired output current and output voltage, and sets the parameter values of the control parameters according to the identified change in the variable load.

[0040] According to this configuration, by setting control parameters based on the output current and output voltage output from the power converter, it is possible to set appropriate control parameters according to the load power of the variable load 17. Therefore, since the AC power output from the power converter can be appropriately supplied according to the variable load 17, it is possible to improve the stabilization of power while making use of the decentralized control of the power converter.

[0041] As a second aspect, in the power converter according to the first aspect, the control parameter includes an inertia constant M for adjusting the frequency fluctuation of the AC power, and the control unit 35 calculates the output AC power and the fluctuation of the AC power based on the acquired output current and output voltage, identifies the magnitude of the variable load based on the calculated fluctuation of the AC power, and sets a larger parameter value of the inertia constant M as the identified variable load is larger.

[0042] According to this configuration, since the parameter value of the inertia constant M can be increased as the variable load is larger, the frequency fluctuation of the AC power output from the inverter 22 can be suppressed, and the improvement of power stabilization can be achieved.

[0043] As a third aspect, in the power converter according to the first or second aspect, the control parameter includes a virtual impedance for adjusting power sharing with the AC power supply unit, and the control unit 51 calculates the output AC power based on the acquired output current and output voltage, identifies a load parameter related to the change pattern of the variable load based on the acquired output current, output voltage, and AC power, and calculates and sets a parameter value of the virtual impedance corresponding to the power sharing based on the identified load parameter.

[0044] According to this configuration, when the fluctuation of the variable load is large, the power sharing of the DC power supply unit can be increased and the power sharing of the AC power supply unit 15 can be decreased, so that the output fluctuation of the AC power supply unit 15 can be alleviated.

[0045] As a fourth aspect, in the power converter according to the first to third aspects, the AC power system includes a plurality of the AC power systems in which the bus 16 is connected to other buses 16 via the tie line 63. The control parameter includes a control gain for controlling the current of the AC power. The control unit 71 calculates the output AC power based on the acquired output current and output voltage, and determines whether the DC power supply unit of the other AC power systems is in a non-operating state based on the acquired output current, output voltage, and AC power. When it is determined that the DC power supply unit is in a non-operating state, the parameter value of the control gain is set so that the responsiveness of the power supply of the AC power supplied to the other AC power systems is increased.

[0046] According to this configuration, even when supplying AC power from the DC power supply unit to the variable load of another AC power system via the power converter, the responsiveness of the power supply can be increased, so that the responsiveness to load fluctuations can be maintained.

[0047] The power systems 10 and 60 according to the fifth aspect include an AC power supply unit, a bus 16 to which the AC power supply unit is connected, a variable load 17 connected to the bus 16, a DC power supply unit (battery 21) connected to the bus 16, and the power converter (inverter 22) that converts the DC power output from the DC power supply unit into AC power and executes virtual synchronous generator control.

[0048] According to this configuration, it is possible to provide a power system capable of stabilizing power while taking advantage of the distributed control of the power converter.

Explanation of Signs

[0049] 10, 60 Power systems 15 AC power supply unit 16 Bus 17 Variable load 18 Load 21 Battery 22 Inverter 31 Ammeter 32 Voltmeter 35, 51, 71 Control Unit

Claims

1. In a power converter that is connected to an AC system including an AC power supply unit, a bus to which the AC power supply unit is connected, and a variable load connected to the bus, and that converts DC power output from a DC power supply unit into AC power, a sensor that detects the output current and output voltage of the output AC power; a control unit that sets a parameter value of a control parameter for executing virtual synchronous generator control based on the detection result of the sensor, and the control unit acquires the output current and the output voltage from the sensor, identifies a change in the variable load based on the acquired output current and output voltage, and a power converter that sets a parameter value of the control parameter according to the identified change in the variable load.

2. The control parameter includes an inertia constant for adjusting a frequency fluctuation of the AC power, and the control unit calculates the output AC power and a fluctuation of the AC power based on the acquired output current and output voltage, identifies a magnitude of the variable load based on the calculated fluctuation of the AC power, and the power converter according to claim 1, wherein the larger the identified variable load is, the larger the parameter value of the inertia constant is set.

3. The control parameter includes a virtual impedance for adjusting power sharing with the AC power supply unit, and the control unit calculates the output AC power based on the acquired output current and output voltage, identifies a load parameter related to a change pattern of the variable load based on the acquired output current, output voltage, and AC power, and the power converter according to claim 1, wherein a parameter value of the virtual impedance corresponding to the power sharing is calculated and set based on the identified load parameter.

4. The AC system is a plurality of the AC systems in which the bus is connected to another bus via a tie line, and the control parameter includes a control gain for controlling a current of the AC power, and the control unit calculates the output AC power based on the acquired output current and output voltage, and determines whether or not the DC power supply unit of the other AC system is in a non-operating state based on the acquired output current, output voltage, and AC power. The power converter according to claim 1, wherein when it is determined that the DC power supply unit is in a non-operating state, the parameter value of the control gain is set so that the responsiveness of the power supply of the AC power supplied to the other AC systems becomes faster.

5. An AC power supply unit, A busbar to which the AC power supply unit is connected, A variable load connected to the busbar, A DC power supply unit connected to the busbar, A power system comprising: the power converter according to any one of claims 1 to 4, which converts DC power output from the DC power supply unit into AC power and executes virtual synchronous generator control.

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